The structure and design of railroad cars typically depend upon the nature of the material being hauled with the cars. Fluids, such as fossil fuels or other liquid chemicals, are typically carried in entirely enclosed liquid tanker cars. Tanker cars include closable openings through which they may be filled. These openings are positioned on the top and are capped to protect the contents of the tanker. The tanker cars also generally include ports carried on their lower side to empty the tankers of the liquid by the force of gravity.
Particulate or granular commodities, such as coal or mineral ores or the like, are generally transported by rail in open-topped railcars. Such open-topped railcars generally have a number of vertical walls extending upwardly from a floor to define a cavity. A number of cross braces frequently extend from a position along a vertical wall downwardly and inwardly to the floor or generally horizontally from one sidewall to another, providing structural support and rigidity to the railroad car. When loading such open-topped railcars, the cars are generally positioned beneath a large hopper and the cargo is loaded through the upper open top of the car; such loading is often referred to as "flood loading". When the railroad car reaches its destination, the cargo may be unloaded through the openings carried in the floor of the car, which may be in the form of a plurality of conical or "V"-shaped depressions that converge downwardly into a flow-control door system carried by the lower portion of the car.
Alternatively, some open-topped cars, referred to as "roll over" or "rotary dumping" cars, may unload product by being pivoted about a central axis to invert the car, thereby emptying its contents through its open top. Such rotary dumping cars may not be adapted to release product through the floor, but do generally include cross braces for support.
Both tanker cars and hopper cars are specifically suited for their intended purposes--tanker cars generally cannot be used for hauling anything but fluids and hopper cars generally cannot be used for hauling anything but granular commodities. As a result, railroad cars frequently carry loads in only one direction, underutilizing their railcars by making a return trip without any cargo. For example, coal cars carry coal from coal mines to a purchaser, but return back to the coal mine empty. Such "deadheading" results in relatively high operating expenses for the railroad (including fuel for transporting empty cars) and high capital costs (for single purpose, dedicated railroad cars which remain empty half of the time).
A number of attempts have been made to convert certain types of vehicles, such as semi-trailers or vans, from a configuration suitable for handling piece goods to configurations for handling bulk materials. For instance, U.S. Pat. No. 4,735,457 (Bonerb et al) and U.S. Pat. No. 4,678,389 (Bonerb) disclose a system for converting a trailer for use with a truck from a piece-good configuration to a bulk material configuration. This design utilizes a plurality of cup-shaped, upwardly open bags attached to a system of pulleys and cables. The pulleys and cables are permanently fixed to and become a part of the structure of the trailer. These pulleys and cables are used to lower these open-topped containers wherein they may be used to haul bulk goods such as grains and to raise and collapse the containers into a compact position disposed against the roof of the trailer. The pulleys and cables include struts which extend from the floor to the roof and are permanently affixed to the floor and the roof to provide both structural integrity and to guide the deployment of the containers as they are raised and lowered with the cables.
U.S. Pat. No. 4,497,259 (Titterton) discloses a flatbed railcar which includes a specially-designed floor. The floor of this car includes a brace which is positioned at the bottom of the car to define its floor when in use as a flatbed. However, this brace may be raised upwardly along guides on the bulkheads of the car to lift a series of flexible containers. This brace includes a series of openings which communicate with the interiors of the containers and a series of discharge ports are carried on the underside of the railcar, with one discharge port being associated with each container. Once the flexible containers have been emptied of their contents through the discharge ports, the brace may be lowered once again, collapsing the containers, such that the brace once again serves as the floor of the flatbed car.
U.S. Pat. No. 4,909,156 (Erickson), issued to one of the inventors of the present invention, discloses a large, flexible bladder for use with open-topped railcars. This bladder is designed to line most or all of the interior of the railcar and includes a filling port positioned at the top of the car and a discharge port positioned adjacent the flow-control valve system carried on the underside of the car. When the railcar is being used to haul materials such as coal, the bladder may be completely collapsed. Although the bladder may be simply carried outside of the railcar, it is also designed to serve as a tarp which covers the material within the railcar. The tarp must be lashed down to the top of the railroad car by a series of cables or the like in order to prevent it from blowing away as the train progresses.
When it is desired to convert the railcar from a configuration for hauling bulk materials such as coal to a liquid-hauling configuration, the bladder may be positioned within the railcar and filled with a liquid or other flowable material. Upon reaching the desired destination, the bag may be emptied through the discharge ports on its underside and the bladder may be rolled up and out of the way so that the car may be filled with granular materials through the car's open top from a silo, as described above.
Thus, attempts have been made to convert a trailer or the like adapted for use with one type of commodity to a configuration suitable for hauling another type of commodity. However, each of the attempts described above have a number of deficiencies.
In the design proposed by Bonerb and Bonerb et al., a rather complex series of pulleys, cables and struts must be used. Since this structure must be permanently affixed to the trailer and relies upon the presence of both a roof and floor of the trailer, such a permanent structure would not be useful for railroad hopper cars or the like which must commonly be filled through an open top and, in the case of rotary dumping cars, must be emptied through the open top as well. Furthermore, adding all of this complex structure to a trailer is rather time consuming and quite expensive, greatly increasing the cost of each individual trailer outfitted with this conversion equipment. Unless a trailer is dedicated to a single route wherein piece goods would be hauled in one direction and bulk materials would be hauled in the other, the cost of adding this conversion may well outweigh the possible benefit of the added capability of hauling grains and the like.
Titterton's flatbed car suffers from many of the same problems associated with Bonerb's design. In particular, the structure of this flatbed car requires that the flexible containers and the supporting brace be a permanent part of the flatbed car. Additionally, a number of cables and pulleys must be utilized to permit the brace/false floor to be raised and lowered between its flatbed configuration and its bulk cargo configuration. The very structure of this flatbed car dictates that the floor of the flatbed must be movable, that a series of ports be provided in this false floor for filling the flexible containers, and that the bottom of the railcar be provided with discharge hoppers. Since standard flatbed cars do not include all of this structure, Titterton's railcar must initially be built according to his invention, i.e., an existing flatbed railcar cannot readily be retrofitted with this invention. As in Bonerb's invention, this requires that the railcar be dedicated to a route that would justify the additional expense of the movable floor and the flexible containers.
Additionally, most open-topped railcars of the type discussed above include cross braces for structural support and rigidity. The presence of such cross braces would prevent one from using a false floor that must be raised and lowered as required by Titterton because the floor's movement would be blocked by the braces.
Erickson's design is adapted to readily retrofit existing open-topped railcars without any significant additional expense. At the most, providing a series of hooks of the like for retention of attachment cables about the periphery of the car and a small bar or the like for retraction of the bladder are all that are required. However, as noted above, a number of open-topped car designs utilize cross braces which may extend into the interior cavity of the car.
When hauling bulk materials such as coal, such braces are not a serious impediment because the coal will simply surround the braces during filling. Cars utilizing such cross braces for structural support essentially preclude the use of a bladder such as that set forth by Erickson, though, without specially constructing an expensive convoluted bag dedicated to use with a single railcar design. Even if one were to specially design such a bladder, the stress concentration on the bladders about these braces and any convolutions in the floor can cause undue wear and reduce the life of the bladder.
Many trains using open-topped cars, such as unit trains used in hauling coal, move continuously, even during filling and emptying of the railcars. For instance, when such cars are unloaded, they are generally indexed forward one car length at a time to properly position a car over the unloading location. Any reduction in the rate at which the trains move through the filling and emptying stations leads to unacceptable disruption or delay of the normal loading and unloading process of the train. The bladder design proposed by Erickson is fairly cumbersome to handle due to its rather large size and must be physically lashed down to the rail cars when used as a tarp, as explained above. This handling difficulty and the process of tying the tarp down can significantly delay a train during the loading and unloading operations.
Thus, it would be desirable to provide a relatively inexpensive mechanism for converting any standard open-topped railcar to a configuration for use in hauling liquids or other flowable materials. In particular, such a design would require that the bladder or bladders be removable from the cargo hold of the railcar so that the car may be filled, and possibly emptied, with existing equipment through an open top, desirably without any significant reduction in the rate of progress of the train. It may also be desirable to provide a cover for such a railcar to minimize the loss of coal or the like as a train proceeds down the track.